Abstract
A 2-year-old, castrated, male Russian blue cat presented with acute dyspnoea, cyanosis, and lethargy. A thoracic radiography revealed a large cranial mediastinal mass; the computed tomography revealed caudal lobe atelectasis of the right lung with pericardial and pleural effusions. The cytodiagnostic tests revealed high-grade CD4(+) CD8(+) T-cell mediastinal lymphoma as clinical stage Vb; l-asparaginase-cyclophosphamide-doxorubicin-vincristine-prednisolone (l-CHOP)-based chemotherapy was initiated, following which the mass shrunk rapidly; 1 week after the initiation of chemotherapy, the appetite-related and respiratory symptoms improved dramatically, and the pleural and pericardial effusion resolved. The patient remains in complete remission three years after the initiation of the l-CHOP chemotherapy. Therefore, the accurate diagnosis and instantaneous initiation of chemotherapy may resolve life-threatening pleural and pericardial effusions in cats with high-grade aberrant T-cell mediastinal lymphoma.